Adjacent segment degeneration after fusion spinal surgery—a systematic review

Purpose: Adjacent segment degeneration (ASDeg) and disease (ASDis) have become major concerns after fusion surgery. However, there is no definitive data or knowledge about the incidence or risk factors. The review discusses the incidence and risk factors and prevention of ASDeg and ASDis in the relevant literature. Methods: We performed a systematic review of meta-analyses, randomized control trials, and cohort studies published in English to provide evidence-based information about ASDeg and ASDis. Results: According to a meta-analysis, the pooled incidence of ASDeg after lumbar and cervical fusion surgery was 26.6% and 32.8%, respectively. Approximately 1/4–1/3 of ASDeg progressed to ASDis. Risk factors after cervical fusion surgery were young age, pre-existing disc degeneration, short fusion segment, high T1 slope, disruption of adjacent soft tissue, and plate placement close to the adjacent disc. The risk factors of ASDeg and ASDis after lumbar fusion surgery were age, genetic factors, high body mass index, pre-existing adjacent segment degeneration, laminectomy at the adjacent level of fusion, excessive distraction of the fusion level, insufficient lumbar lordosis, multilevel fixation, floating fusion, coronal wedging of L5-S disc, pelvic tilt, and osteoporosis. Motion-preserving surgeries seem to have less risk of ASDeg and ASDis than conventional fusion surgery both in the lumbar and cervical spine. Conclusions: The existent literature points out variables involved in ASDeg and ASDis. High evidence-level studies should provide more relevant data to guide strategies for avoiding ASDeg and ASDis.